#include "stdio.h"
#include "stdlib.h"

int getSum(int);

int main()
{
    int n;

    scanf("%d", &n);

    printf("sum = %d\n", getSum(n));

    return 0;
}

int getSum(int n)
{
    int i = 0;
    int sum = 0;

    while (i < n)
    {
        sum += (i + 1);

        i ++;
    }

    return sum;
}
